Tanning process.



I STATES FRANZ WALTER WARTENBERGER, OF HAMBURG, GERMANY.

TANNING PROCESS.

SPECIFICATION forming part of Letters Eatent No. 644,482, dated February 2'7, 1900.

Application filed March 23,1899. Serial No. 710,223. (No specimens.)

To all whom it may concern:

Be it known that I, FRANZ WALTER WAR- TENBERGER, a subject of the German Emperor, and a resident of Hamburg, in the Ger man Empire, have invented a certain new and useful Improved Tanning Process, of which the following is a specification.

My invention has relation to the art of tanning; and it has for its object a process where by the tanning may be effected in a most expeditious and yet thorough manner, the process consisting, essentially, in subjecting hides previously prepared for tanning by the usual liming and bating processes to the action of a weak aqueous solution of picric acid, after which the tanned hides are subjected to the action of a solution of hyposulfite of soda, (Na S O SI-I O,) or other reagent capable of fixing the picric acid, the tanned hides being then finished for market by beating, rubbing, scraping, &c., in the usual manner. The essential feature of this invention lies, therefore, in the use of highly-diluted solutions of picric acid, the strongest solution which may be advantageously used containing about one part of picric acid to about seventy parts of water, though I prefer to use even Weaker solutions.

The use of picric acid as a tanning agent is not practicable except in the form of such weak solutions as above referred to, not only on account of the cost involved, but because the picric acid unduly attacks and deteriorates the hides or skins, which is not the case when solutions of the character referred to are used, while the cost involved is very moderate.

The process in itself is simple, and consists in steeping the hides or skins previously preparedi. a, by the usual liming and bating processes-in a weak solution of picric acid (as explained above) at ordinary temperature, which in some cases may be raised to about 30 centigrade and maintained at this temperature during the process of tanning. The duration of the tanning process or tanning operation depends upon the nature and weight of the hides and varies accordingly. I have,

however, found that good leather is obtained by subjecting the hides to the action of the said diluted picric-acid solution generally for from about two to four hours. When the hides are thoroughly tanned and converted into leather, they are removed from the tanning liquor and subjected to a subsequent treatment, which consists in rinsing the hides or leather proper in a solution of about one hundred parts of water and about thirty parts of hyposulfite of soda, (Na S O 51 1 0,) or other agent capable of fixing picric acid. The hyposulfite solution has the effect of giving the tanned leather a slightly-lighter shade than usual, of fixing the picric acid, and of depriving the latter of its discoloring and poisonous properties. After this treatment the leather is washed and then curried in the usual manner.

Heretofore wherever phenols (to which also belongs picric acid) have been employed in the tanning process it has only occurred in combination with other chemical agents. For example, it has been proposed to employ carbolic acid in connection with alum, culinary salt, (sodium chlorid,) aluminium salts, and the like for tanning purposes; but here the carbolic acid only plays a secondary part. Taken by itself the carbolic acid is devoid of tanning qualities, as has been frequently demonstrated by experiment. Among the phenols, however, picric acid has been found to constitute a quick-acting and useful tanning agent, provided it is used, as hereinbefore described, in weak solutions.

Having thus described my invention, what I claim as new therein, and desire to secure by Letters Patent, is

1. The process,which consists in subjecting hides or skins previously prepared for tanning by the usual processes, to the action of a solution of about one part of picric acid and of about seventy parts of water, for the pur pose set forth.

2. The process,which consistsin subjecting hides orskins, previously prepared for tanning by the usual processes, to the action of a weak solution of picric acid and then to the action of a solution of hyposulfite of soda, for the purposes set forth.

FRANZ WALTER WARTENBERGER.

Witnesses:

ALEXANDER SPEOHT, E. H. L. MUMMENHOFF. 

